Canned linear motor

ABSTRACT

A canned linear motor such that increase of the temperature of the mover is suppressed, the viscous damping force is reduced, and the strength of the can does not deteriorate. A canned linear motor comprises two parts, in one of which a permanent magnet is provided as a field system and in the other of which a three-phase armature winding, a winding fixing frame for supporting the armature winding, a coolant passage through which a coolant for cooling the surfaced of the armature winding passes, a can ( 14 ) covering the armature winding and the coolant passage, and a header ( 14 ′) for sealing the can. Slits ( 151, 152 ) extending in the direction of travel and parallel to each other are formed in the can ( 14 ).

TECHNICAL FIELD

[0001] The invention relates to a linear motor, and in particular acanned linear motor, used for, for example, feeding in electroniccomponent inspection apparatuses and machine tools, etc., in which anincrease in temperature is suppressed and constant-rate feeding accuracyis required.

PRIOR ARTS

[0002] In a canned linear motor provided with three-phase armaturewinding at its stator and a permanent magnet, used as a field system, atits mover, the armature winding is directly cooled by a coolant, whereinan increase in the surface temperature of the linear motor can besuppressed to be low.

[0003] However, according to the conventional art, since there iscompletely no problem if a structure in which a mover and a stator arereplaced with each other is employed, such a type in which the mover isprovided with armature winding has been frequently used in applicationswhere the stroke is long.

[0004] Herein, a description will be given mainly of a canned linearmotor in which an armature winding formed of a plurality of coil groupsis made into a mover, and a plurality of permanent magnets of which usedfield systems, which have different polarities from each other arejuxtaposed adjacent to a stator. However, the canned linear motor is notlimited to this specification.

[0005]FIG. 8 is a perspective view showing the entirety of a linearmotor in a conventional art. In FIG. 8, reference number 80 denotes amover, reference number 81 denotes a mover base, reference number 84denotes a can, reference number 31 denotes a coolant discharge port,reference number 32 denotes a coolant supply port, reference number 33denotes a cable, reference number 90 denotes a stator, reference number91 denotes a stator base, reference number 92 denotes a field systemyoke, and reference number 93 denotes a permanent magnet.

[0006] The mover 80 is formed to be T-shaped as described later, whereinits longitudinal member (armature) is supported by a linear guide, anair slider, and a slider guide, etc., between the permanent magnets 93disposed between the field system yokes 92 and 92 of the stator 90, andby causing an appointed current to flow into the armature winding, thelongitudinal member operates with a magnetic field produced by thepermanent magnets 93 to generate a thrust in the mover 80, by which themotor 80 is movable in the directions of travel shown by the arrows.

[0007]FIG. 1(b) is a cross-sectional view of a conventional art linearmotor of FIG. 8 when observing the same from the front side thereof. Inthe drawing, the mover 80 is formed to be T-shaped. The mover 80 iscomposed of a mover base 81, a can 84 supported in a depression of themover base 81 downward, a header 84′ (See FIG. 5) to seal the can 84, awinding fixing frame 82 disposed in a gap produced by the can 84 and theheader 84′, a coreless type three-phase armature winding 83, which isfixed at the winding fixing frame 82, and a coolant passage 87 passingthrough the can 84.

[0008]FIG. 5(a) shows a side elevational view of the mover, and FIG. 6shows a view of arranging an armature winding when being observed fromthe mover side. Herein, as shown in FIG. 6, the armature winding 83 isformed of three phases and is thin plate-shaped. By adhering the same toboth the right and left sides of the winding fixed frame 82, theentirety of the armature winding is constructed, and the strengththereof is improved. Also, since the winding fixing frame 82 itselfneeds strength, the winding fixing frame 82 is frequently made ofstainless steel.

[0009] The can 84 is rectangular-tubular, for which a stainless steelthin plate is bent to be channel-shaped and welded together. Two headers84′ (FIG. 5) made of stainless steel casting are provided with a coolantsupply port 32 and a coolant discharge port 31, through which a coolantis permitted to pass. The can 84 and headers 84′ are welded together atthe conjunction plane.

[0010] Also, by causing a coolant to be supplied through the coolantsupply port 32 and to be discharged through the coolant discharge port31, the coolant flows through a coolant passage 87 (FIG. 1(b)) locatedbetween the armature winding 83 and the can 84.

[0011] On the other hand, as shown in FIG. 1(b), the stator 90 isrecess-shaped so that it can wrap the armature portion of the mover 80.The stator 90 is composed of a permanent magnet 93 disposed at bothsides of the can 84 and header 84′ of the mover 80 with a gap, a fieldsystem yoke 92 made of a magnetic body that causes a magnetic fluxproduced by the permanent magnet 93 to pass through, and a stator base91 to support the same. Also, a plurality of permanent magnets 93juxtaposed in the direction of travel are disposed so that the same havea different polarity from each other at each polarity pitch λ (FIG. 8).

[0012] The canned linear motor thus constructed operates with a magneticfield produced by the permanent magnet of the stator by causing anappointed current appropriate to a position of the mover to flow intothe armature winding, wherein a thrust is generated at the mover, andthe armature winding heated due to a copper loss is cooled by thecoolant, and a temperature rise at the surface of the mover can besuppressed to be low.

[0013] However, in the conventional art, there are the followingproblems.

[0014] The can 84, winding fixing frame 82, header 84′, etc., are madeof stainless steel as described above. The members made of stainlesssteel materials generate an eddy current ie at each polarity pitch λ bypassing between the permanent magnets 93 of the stator 90. FIG. 5(b)shows a view of an occurrence of the eddy current ie. As has been madeclear in FIG. 5(b), the eddy current ie of the conventional art deviceflows, depicting a large loop, so that the flow passage extends entirelyin the vertical direction of the can 84 and header 84′. And, a viscousdamping force is generated by vertical direction constituents of theeddy current ie. The viscous damping force crosses the magnetic fluxproduced by the eddy current ie and permanent magnet 93 and is generatedin a reverse direction of the direction of travel of the mover 80. Theintensity thereof is almost proportionate to the thickness and width ofstainless steel, travel speed of the mover 80, number of points wherethe eddy current ie occurs, and square of the magnetic flux density. Thefollowing problems further occur due to generation of such a viscousdamping force.

[0015] (1) Where a certain thrust is attempted to be gained, the thrustis decreased equivalent to the size of the viscous damping force even ifan appointed armature current is caused to flow, wherein it becomesnecessary to cause a greater armature current to flow than is usuallynecessary. Resultantly, the copper loss of the armature winding isincreased, temperature of the can and the surface of the header isaccordingly increased.

[0016] (2) The eddy current is converted to heat as a so-called eddycurrent loss at a point where an eddy current is generated. That is, thecan, winding fixing frame and header where the eddy current is generatedare heated, resulting in a further rise in temperature. In applicationswhere the temperature is remarkably limited, there may be a case whereno expected specification can be satisfied by the heating.

[0017] (3) Recently, a viscous damping force has tended to be furtherincreased in line with a request for increasing the speed, and furtherthe viscous damping force is generated in a reverse direction of thetravel direction of the mover, wherein the speed of a linear motor issubjected to fluctuations due to fluctuations of the viscous dampingforce. Since influences of the viscous damping force onto fluctuationsin the speed of the linear motor are comparatively slight in comparisonwith a thrust generated, the influences are not highly emphasized.However, in recent years, requests to decrease fluctuations in the speedhave increased in line with recent needs for high accuracy and highdensity in various types of precious machines and apparatuses, etc.Therefore, it has been required that, without changing the materials ofcomponents, fluctuations in the speed of a linear motor are suppressedand decreased while suppressing the fluctuations in the viscous dampingforce with mechanical strength maintained.

[0018] The invention was developed in order to solve these and otherproblems, and it is therefore an object of the invention to provide acanned linear motor that is capable of suppressing a rise in thetemperature of the mover, decreasing the viscous damping force, andsuppressing the ratio of fluctuations, and in which the strength of thecan does not deteriorate.

DISCLOSURE OF THE INVENTION

[0019] In order to solve the above-described problems, a canned linearmotor according to the first aspect of the invention is featured in thatthe canned linear motor includes field system yokes, having differentpolarities from each other, in which a plurality of permanent magnetsare juxtaposed adjacent to each other; an armature disposed so as to beopposed to the above-described permanent magnet row with a magnetic gapsecured therebetween and having an armature winding; in which theabove-described armature is provided with a winding fixing frame havingthe above-described armature winding mounted on both sides thereof alongthe lengthwise direction of the above-described armature; a can thataccommodates the above-described armature winding and theabove-described winding fixing frame and has a coolant passage forcausing a coolant to flow to the periphery of both the members; and aheader having a coolant supply port attached at one of both ends of theabove-described can and having a coolant discharge port attached at theother end thereof; and in which any one of the above-described fieldsystem yokes and the above-described armature is made into a stator, andthe other of which is made into a mover, and the above-described fieldsystem yokes and the above-described armature are caused to run relativeto each other; wherein a plurality of slits are provided in theabove-described can, a leak preventing sheet is adhered to the inside ofthe above-described can so as to cover the above-described slits; and atthe same time, resin is filled in the above-described slits.

[0020] Further, a canned linear motor according to the second aspect ofthe invention is featured in that, in addition to the canned linearmotor described in the first aspect of the invention, theabove-described plurality of slits extend in the direction of travel inparallel to each other.

[0021] Also, a canned linear motor according to the third aspect of theinvention is featured in that, in addition to the canned linear motordescribed in the first aspect of the invention, the above-describedplurality of slits are split in parallel to each other and in thedirection of travel.

[0022] In addition, a canned linear motor according to the fourth aspectof the invention is featured in that, in addition to the canned linearmotor described in the first or third aspect of the invention, theabove-described plurality of slits are disposed one by one every 3×λ(λ=polarity pitch).

[0023] Also, a canned linear motor according to the fifth aspect of theinvention is featured in that, in addition to the canned linear motordescribed in the first, third or fourth aspect of the invention, theabove-described plurality of slits are split in parallel to each otherand in the direction of travel, and a deviation of 1.5×λ (λ=polaritypitch) is provided between the above-described slits and adjacent slitsin the direction orthogonal to the direction of travel.

[0024] Further, a canned linear motor according to the sixth aspect ofthe invention is featured in that, in addition to the canned linearmotor described in any one of the first through the fifth aspects of theinvention, the above-described header is provided with a plurality ofslits extending in parallel to each other in the travel direction, and aleak preventing sheet is adhered to the inside of the above-describedheader so as to cover the above-described slits, and at the same time,resin is filled in the above-described slits.

[0025] And, a canned linear motor according to the seventh aspect of theinvention is featured in that, in addition to the canned linear motordescribed in any one of the first through the six aspects of theinvention, the above-described winding fixing frame is provided withslits extending in parallel to each other.

[0026] Further, a canned linear motor according to the eighth aspect ofthe invention is featured in that the canned linear motor includes fieldsystem yokes, having different polarities from each other, in which aplurality of permanent magnets are juxtaposed adjacent to each other; anarmature disposed so as to be opposed to the above-described permanentmagnet row with a magnetic gap secured therebetween and having anarmature winding; in which the above-described armature is provided witha winding fixing frame having the above-described armature windingmounted on both sides thereof along the lengthwise direction of theabove-described armature; a can that accommodates the above-describedarmature winding and the above-described winding fixing frame and has acoolant passage for causing a coolant to flow to the periphery of boththe members; and a header having a coolant supply port attached at anyone of the both ends of the above-described can and having a coolantdischarge port attached at the other end thereof; and in which theabove-described field system yokes are made into a stator and theabove-described armature winding is made into a mover, and theabove-described field system yokes and the above-described armature arecaused to run relative to each other; wherein the entire length L of theabove-described can is defined as follows:

L=(n+1/2)λ

[0027] where L is the entire length of the can, λ is a polarity pitch ofthe permanent magnets, and an integer is n.

[0028] With the above-described construction, since the number of pointswhere an eddy current occurs is made constant, and fluctuations of aviscous damping force are remarkably suppressed, it becomes possible toreduce fluctuations in the speed of a linear motor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a cross-sectional view of a canned linear motor whenbeing observed from the front side; wherein (a) shows a case of theinvention, and (b) shows a case of the conventional art;

[0030]FIG. 2 shows a mover according to a first embodiment of theinvention; wherein (a) is a side elevational view of a mover, and (b) isa view showing an occurrence of an eddy current at the side of themover;

[0031]FIG. 3 shows a can according to the invention; wherein (a) is anenlarged view showing a cross section of the can according to the firstembodiment, and (b) is an enlarged view showing a cross section of thecan according to a third embodiment;

[0032]FIG. 4 shows a mover according to a second embodiment of theinvention; wherein (a) is a side elevational view of a mover, and (b) isa view showing an occurrence of an eddy current at the side of themover;

[0033]FIG. 5 shows a mover in a conventional art; wherein (a) is a sideelevational view of the mover, and (b) is a view showing an occurrenceof an eddy current at the side of the mover;

[0034]FIG. 6 is a view showing the interior of the mover when beingobserved from the side in the conventional art;

[0035]FIG. 7 is a view comparing a viscous damping force according tothe first embodiment with that according to the conventional art;

[0036]FIG. 8 is a perspective view of a canned linear motor according tothe conventional art;

[0037]FIG. 9 is a perspective view showing the entire linear motorhaving a cooling can according to the third embodiment of the invention;

[0038]FIG. 10 is a sketch describing the condition of points where aneddy current occurs, according to the invention;

[0039]FIG. 11 is a sketch describing the condition of points where aneddy current occurs, according to the conventional art; and

[0040]FIG. 12 is a view comparing a viscous damping force the accordingto the third embodiment of the invention with that of the conventionalart.

BEST MODE FOR CARRYING OUT THE INVENTION

[0041] [Embodiment 1]

[0042] Hereinafter, a description is given of the first embodiment ofthe invention with reference to FIG. 1 through FIG. 3.

[0043]FIG. 1(a) is a cross-sectional view of a canned linear motor ofthe invention when being observed from the front side, FIG. 1(b) is across-sectional view of a canned linear motor of the conventional artwhen being observed from the front side. FIG. 2(a) is a side elevationalview of a mover, and (b) is a view showing an occurrence of an eddycurrent at the side of the mover.

[0044] A stator 20 is recess-shaped so that the armature portion of amover 10 is placed between the sides of the stator 20. The stator 20 iscomposed of field system yokes 22 made of a magnetic body and a statorbase 21 to support the yokes 22, wherein the field system yokes permit amagnetic flux to pass therethrough, in which the magnetic flux isproduced by a plurality of permanent magnets 23 disposed at both sidesof a can 14 of the mover 10 and header 14′ thereof with a magnetic gap.Also, a plurality of permanent magnets 23 juxtaposed in the direction oftravel are disposed so that the permanent magnets 23 have a differentpolarity from each other at every polarity pitch λ (FIG. 9).

[0045] As in the conventional art, the mover 10 is T-shaped in FIG.1(a). The mover 10 is composed of a three-phase thin plate type armaturewinding 13 (FIG. 6), a winding fixing frame 12, a coolant passage 17, acan 14 to cover these members, a header 14′ (FIG. 2) to seal the can 14,and a mover base 11 to support the can 14.

[0046] By attaching the armature winding 13 to both right and left sidesof the winding fixing frame 12, the strength of the entire armaturewinding is improved. Also, since strength is required at the windingfixing frame 12 itself, the winding fixing frame 12 is made of astainless steel material.

[0047] The can 14 is produced by bending a thin stainless steel platelike a channel and welding it together so as to make it rectangularlytubular. Two headers 14′ (FIG. 2) similarly formed of stainless steelcasting are, respectively, provided with a coolant supply port 32 and acoolant discharge port 31 in order to permit a coolant to pass through.The can 14 and headers 14′ are welded together at the conjunction planethereof.

[0048] The mover 10 thus constructed is supported by a linear guide, anair slider, a sliding guide, etc., which are not illustrated, and iscaused to move in the direction of travel.

[0049] In addition, by supplying a coolant through the coolant supplyport 32 and discharging the same through the coolant discharge port 31,the coolant flows through a coolant passage 17 located between thearmature winding 13 and the can 14, whereby since the coolant suppliedthrough the coolant supply port 32 passes through the coolant passage 17while capturing heat from the armature winding 13, and is dischargedthrough the coolant discharge port 13, it is possible to suppress atemperature rise at the surface of the linear motor. The dischargecoolant is cooled down by a cooling device (not illustrated) andre-circulated.

[0050] Points of difference from the conventional arts reside in thatthe can 14 is provided with a plurality of slits 151 and 152 extendingin parallel to each other and in the direction of travel.

[0051] Also, the headers 14′ are provided with more slits 15 extendingin parallel to each other and in the direction of travel than the slitsin the can 14.

[0052] Further, in order for the coolant not to leak through these slits15, 151 and 152, a leak preventing sheet 16 (FIG. 3) is adhered to thecan 14 with an adhesive agent 18 or adhesive agent 19 is filled in theslits. Also, the adhesive agent 18 and adhesive agent 19 may be the samematerial.

[0053] The slits 15 are holes that are cut open to be long and narrow inthe direction of travel of the mover 10. The can 14 is provided withslits 151 and 152 that are divided into two stages in the heightdirection. Provision of a number of slits 151 and 152 in the can 14 madeof a thin plate results in deterioration of the strength while loweringan eddy current ie. Since the headers 14′ are provided with an end faceand have allowance in strength, slits 15 are provided in four stages inthe height direction.

[0054] In addition, as shown in FIG. 3(a), the leak preventing sheet 16is adhered to two surfaces (in the drawing, only one surface isillustrated) facing the coolant passage 17 in the header tube of the can14, so that the coolant flowing through the coolant passage 17 does notleak out of the slits 15.

[0055] Further, to prevent the mechanical strength from being lowereddue to provision of the slits 15, as shown in FIG. 3(b), resin such asthe adhesive agent 19 is filled in the slits 15, wherein even if a crackis produced in the leak preventing sheet 16, the coolant does not leakfrom the slits 15.

[0056]FIG. 2(b) shows how an eddy current ie occurs in the mover thusconstructed. As has been made clear by comparing the above with FIG.5(b) that is a view showing an occurrence of an eddy current in theconventional art, the eddy current ie produced by the invention issubdivided because the flow passage thereof is interrupted by the slits151 and 152, whereby since vertical direction components of the eddycurrent ie are segmented, the viscous damping force can be made small.

[0057] Resultantly, since it is not necessary to generate a thrust forthe viscous damping force, the copper loss is lowered, wherein it ispossible to reduce a temperature rise of the mover. And, since the eddycurrent loss is decreased, it is possible to reduce heat of the can,header and winding fixing frame, which are locations where the eddycurrent loss is produced.

[0058] Next, FIG. 7 shows a comparison of a viscous damping force in theconventional art with that of the invention.

[0059]FIG. 7 shows the mover position—viscous damping forcecharacteristics (unit: N) in a canned linear motor whose thrust isalmost 400N (Newton) and speed is 0.2 m per second. According to thedrawing, the viscous damping force according to the invention shiftsaround 3N while the viscous damping force according to the conventionalart shifts around 9N, wherein the viscous damping force can be loweredto one-third in comparison with the conventional art.

[0060] The above-described embodiment was described, in which slits 15are provided in only the can 14 and header 14′. A number of slits may besimilarly provided in the winding fixing frame 12 (FIG. 1(a)).

[0061] Also, the above structure is such that the mover 10 is providedwith the armature winding 13, and the stator 20 is provided withpermanent magnets 23 which are field systems. An inverted structure isacceptable. Further, although the stator 20 is recess-shaped, such astructure, in which permanent magnets 23 are provided at only a singleside, is acceptable.

[0062] [Embodiment 2]

[0063] Next, a description is given of the second embodiment of theinvention.

[0064]FIG. 4 shows a mover according to the second embodiment of theinvention, wherein (a) is a side elevational view of the mover, and (b)is a view showing an occurrence of an eddy current at the side of themover.

[0065] A point which is different from the first embodiment resides inthe provision of slits. That is, as shown in FIG. 4(a), although slitsextending in parallel to each other and in the direction of travel arecontinuous in the direction of travel in the first embodiment, the slitsare discontinued here in the second embodiment. All other points areidentical to those of the first embodiment.

[0066] In the same drawing, an interval between the end portion of theslit 151 and the corresponding end portion of the slit 153 is 3×λ wherethe polarity pitch of permanent magnets is λ as shown in FIG. 9, theentire length of the slits 151 and 153 is slightly shorter than 3×λ inthe direction of travel, wherein differences are made into discontinuousportions. Also, a slip of 1.5×λ exists between those and the slits 152adjacent thereto in the direction orthogonal to the direction of travel.

[0067]FIG. 4(b) shows how an eddy current ie occurs in the mover inwhich such slits are formed.

[0068] As has been made clear in the same drawing, since the flowpassage is interrupted by the slits 151, 152 and 153, the eddy currentie is subdivided, wherein since the vertical direction components of theeddy current ie are also segmented, the viscous damping force isremarkably reduced in comparison with the conventional art.

[0069] However, since eddy current ie′, which is slightly longer in thevertical direction than the eddy current ie, is produced in thediscontinuous portions of the slits, wherein if the second embodiment iscompared with the first embodiment with respect to only the eddy currentie, the former is slightly inferior to the latter in a lowering of theviscous damping force. However, the mechanical strength of the formercan be remarkably increased by the discontinuous portions, and totally,the second embodiment overcomes the first embodiment.

[0070] All other points are the same as those of the first embodiment.That is, slits may be provided at the headers 14′ and winding fixingframe 12 (FIG. 1(a)), a leak preventing sheet 16 or a thin plate of aninsulating material may be adhered to the inside of the can 14 andheader 14′, and adhesive agent 19 is filled in the slits 15. All ofthese are the same as those in the first embodiment.

[0071] Although, in the above description, the side in which permanentmagnets are provided is made into a stator, and the side in which theabove-described armature winding is provided is made into a mover, it isneedless to say that the invention can be realized if, on the contrary,the side where the permanent magnets are provided is made into themover, and the side where the armature winding is provided is made intothe stator.

[0072] [Embodiment 3]

[0073] Next, a description is given of the third embodiment of theinvention with reference to FIG. 9 through FIG. 12.

[0074]FIG. 9 is a perspective view of the entire linear motor having acooling can according to the third embodiment of the invention. In thethird embodiment, the entire length of the can 14 of the mover 10 isdefined as in Expression (1);

L=(n+1/2)λ  (1)

[0075] where n is an integer, and λ is a polarity pitch of the permanentmagnets.

[0076] Except for the above definition, the third embodiment isidentical to the conventional device in terms of structure, wherein anoverlapping description is omitted. Also, the stator 20 is not changedfrom the conventional device with respect to the shape and structure.

[0077]FIG. 10 is an exemplary view showing the condition where a linearmotor according to the third embodiment is observed from above (themover side) and is a sketch showing the condition of the points (circlesindicated by a broken line) where an eddy current occurs, according tothe positions (A, B, C and D) of the mover can 14.

[0078] In the same drawing, it is understood that the points where aneddy current occurs are four at the position A of the mover can 14. Asin the above, there are four points where an eddy current occurs, at theposition B of the mover can 14. Further, it is understood that therefour points where an eddy current occurs, at positions C and D of themover can 14. That is, since the entire length L of the mover can 14 isdefined as in Expression (1), points where an eddy current occurs arestabilized to be four at any position of the mover can 14. The longerthe entire length L of the can becomes, the greater the increase in thenumber of points where an eddy current occurs. However, the number ofthe points does not fluctuate.

[0079] On the other hand, FIG. 11 is an exemplary view showing thecondition where an eddy current occurs, at the position of the mover inthe conventional art linear motor. FIG. 11 shows a case where the entirelength L of the mover can 14 is established to be L=nλ. In the samedrawing, although there are three points where an eddy current occurs atthe position A of the mover can 14, there are four points at theposition B, and there are three points at the position C again. Also,there are four points at the position D again. That is, since the entirelength L of the mover can 14 is established to be L=nλ, the number ofpoints where an eddy current occurs fluctuates according to thepositions where the mover can 14 is placed.

[0080] Next, FIG. 12 shows a comparison between fluctuations in theviscous damping force according to the conventional art and thoseaccording to the invention.

[0081]FIG. 12 shows fluctuations in the viscous damping force when thespeed is 0.2 m per second in a linear motor whose rated thrust isapprox. 450N. The conventional product is a linear motor, produced byour company (YASKAWA ELECTRIC), for which the entire length of the movercan is almost integral multiple with the pitch of the permanent magnets.In the same drawing, in the case of the conventional product, theminimum value of the viscous damping force is roughly 11N, and themaximum value thereof is roughly 13N, wherein it is understood that thefluctuation is 2N. On the other hand, in the case of the invention, theminimum value of the viscous damping force is roughly 11N, and themaximum value thereof is roughly 12N, wherein the fluctuation is 1N.Therefore, according to the invention, the fluctuation of the viscousdamping force is reduced from 2N to 1N, and is lowered to approx.one-second.

[0082] In addition, in a movable magnet type linear motor in which themover is set at the field system side, since the can is always providedin a magnetic flux, and the amount of occurrence of an eddy current doesnot fluctuate, no fluctuation in the viscous damping force occurs.Therefore, no influence is applied to the invention.

[0083] [Industrial Applicability]

[0084] The invention is applied to a linear motor that is used for atransfer system of factory automation apparatus, for example, tablefeeding of a machine tool, and in particular, the invention is useful inthe field of providing linear motors which can reduce the viscousdamping force, and to lower a fluctuation in speed without lowering themechanical strength characteristics.

What is claimed is:
 1. A canned linear motor including: field systemyokes, having different polarities from each other, in which a pluralityof permanent magnets are juxtaposed adjacent to each other; an armaturedisposed so as to be opposed to said permanent magnet row with amagnetic gap secured therebetween and having an armature winding; inwhich said armature is provided with a winding fixing frame having saidarmature winding mounted on both surfaces thereof along the lengthwisedirection of said armature; a can that accommodates said armaturewinding and said winding fixing frame and has a coolant passage forcausing a coolant to flow to the surrounding of both the members; and aheader having a coolant supply port attached at one of both ends of saidcan and having a coolant discharge port attached at the other endthereof; and in which any one of said field system yokes and saidarmature are made into a stator, and the other of which is made into amover, and said field system yokes and said armature are caused to runrelative to each other; wherein a plurality of slits are provided insaid can, a leak preventing sheet is adhered to the inside of said canso as to cover said slits; and at the same time, resin is filled in saidslits.
 2. The canned linear motor according to claim 1, wherein saidplurality of slits extend in the direction of travel in parallel to eachother.
 3. The canned linear motor according to claim 1, wherein saidplurality of slits are split in parallel to each other and in thedirection of travel.
 4. The canned linear motor according to claim 1 or3, wherein said plurality of slits are disposed one by one every 3×λ(λ=polarity pitch).
 5. The canned linear motor according to claim 1, 3or 4, wherein said plurality of slits are split in parallel to eachother and in the direction of travel, and a slit of 1.5×λ (λ=polaritypitch) is provided between said slits and adjacent slits in thedirection orthogonal to the direction of travel.
 6. The canned linearmotor according to any one of claim 1 through claim 5, said header isprovided with a plurality of slits extending in parallel to each otherin the travel direction, and a leak preventing sheet is adhered to theinside of said header so as to cover said slit, and at the same time,resin is filled in said slits.
 7. The canned linear motor according toany one of claim 1 through claim 6, wherein said winding fixing frame isprovided with slits extending in parallel to each other.
 8. A cannedlinear motor includes field system yokes, having different polaritiesfrom each other, in which a plurality of permanent magnets arejuxtaposed adjacent to each other; an armature disposed so as to beopposed to said permanent magnet row with a magnetic gap securedtherebetween and having an armature winding; in which said armature isprovided with a winding fixing frame having said armature windingmounted on both surfaces thereof along the lengthwise direction of saidarmature; a can that accommodates said armature winding and said windingfixing frame and has a coolant passage for causing a coolant to flow tothe periphery of both the members; and a header having a coolant supplyport attached at any one of both ends of said can and having a coolantdischarge port attached at the other end thereof; and in which saidfield system yokes are made into a stator and said armature winding ismade into a mover, and said field system yokes and said armature arecaused to run relative to each other; wherein the entire length L ofsaid can is defined as follows: L=(n+1/2)λ where L is the entire lengthof the can, λ is a polarity pitch of the permanent magnets, and aninteger is n.